1. Field of the Invention
The present invention relates to an electrically-operated injection molding machine having servomotors as drive sources for various operating sections, and more particularly to a software servo control apparatus for use in an electrically-operated injection molding machine, which is capable of changing servo control variable constants and has a great versatility, and is further capable of performing appropriate torque control.
2. Description of the Related Art
Typically, a conventional electrically-operated injection molding machine is provided with hardware servo circuits each including a position control unit, a speed control unit, and an electric current control unit, for controlling position, speed, and torque of each of plural servomotors associated with various operating sections of the injection molding machine. Also, it has been known to employ a servo circuit of a type having a torque limit means arranged between the speed control unit and the electric current control units for restricting the output torque of an associated servomotor to a commanded torque limit value.
The injection molding machine includes various operating sections such as an injection mechanism, a mold clamping mechansim, etc.; that is, it includes various control axes such as an injection axis, a screw rotation axis, a clamp axis, etc. Therefore, conventionally, it has been necessary to provide the above-mentioned hardware servo circuits for respective axes. Moreover, to change various servo control variable constants which determine reponse characteristics of various sections of a servo system, and the like, replacement of part or all of servo circuit components is required. In addition, since the unit of the torque limit value for presure control is determined in dependence on the hardware arrangement which forms the pressure control system, there is a restriction in improving accuracy in pressure control.